Examples of a currently-used radiation detector include an X-ray detector. See, for example, Japanese Patent Publication No. 2005-019543A. The X-ray detector is provided in an X-ray fluoroscopy apparatus along with an X-ray tube.
The X-ray detector has two types in terms of detecting X-rays. That is, the two types are indirect conversion and direct conversion types. In the indirect conversion-type X-ray detector, incident X-rays are converted into another type of light with scintillators, and then the light is converted into electric charge with a photodiode or a CCD image sensor, whereby X-rays are detected. In contrast to this, in the direct conversion-type X-ray detector, incident X-rays are converted into electric charge with a semiconductor film, whereby X-rays are detected.
With the indirect conversion-type detector, an X-ray reaction position of the scintillator is shifted from a position where a photodiode catches X-rays. In contrast to this, with the direct conversion-type detector, electric charge (electrons or holes) drift from an X-ray reaction position to collecting electrodes in the semiconductor film directly. Consequently, the direct conversion-type detector achieves position resolution superior to that of the indirect conversion-type detector.
A pixel detector is typically used for such an X-ray detector. The pixel detector is formed by a large number of X-ray detecting elements for detecting X-rays in a planar state. The number of X-ray detecting elements corresponds to the number of pixels. Moreover, the pixel detector adopts an integral reading system. That is, electric charge converted from X-rays are stored in a storage capacitor for a given period of time, and thereafter the stored electric charge are read out with a switching element such as a TFT (thin-film transistor). Instead of the integral reading system, a photon counting detector has been adopted widely. The photon counting detector is used also for certain medical devices.
Examples of the photon counting detector include a strip detector 101 as illustrated in FIG. 1. The strip detector 101 includes an n-type semiconductor film 103 that is sensitive to incident X-rays to generate electric charge, and strip electrodes 105 and 107 in X- and Y-directions, respectively, across the semiconductor film 103. The strip electrodes 105 and 107 are elongated plate electrodes. The strip electrodes 105 and the strip electrodes 107 are each in parallel arrangement.
Moreover, the strip detector 101 in FIG. 1 includes p+ layers 171 between the strip electrodes 105 elongated in the X-direction and the semiconductor film 103. The p+ layer 171 is elongated in the X-direction. The strip detector 101 further includes n+ layers 173 between the strip electrodes 107 elongated in the Y-direction and the semiconductor film 103. The n+ layer 173 is elongated in the Y-direction. Moreover, p+ layers 175 are each provided between two adjacent n+ layers 173. Insulating layers 177 (e.g., SiO2: silicon dioxide) are formed in a portion of the semiconductor film 103 where no strip electrode 105 and 107 is formed.
For instance, the strip detector is used for minute observation with a microfocused X-ray tube in a nondestructive inspecting apparatus as industrial equipment. Specifically, the microfocused X-ray tube is used, and when a two-dimensional sensor has a narrow sensitive region, the strip detector is used since less X-rays enter.
Japanese Patent Publications No. 2013-140962A and 2013-140975A each disclose a method of forming photodiode arrays on a silicon wafer using a through-silicon-via (TSV: through silicon via) electrode technique.